C# 15 preview: union types, closed hierarchies and labeled break

C# 15 will add union types that combine a fixed set of types without inheritance or interfaces, plus closed hierarchies that block inheritance from other assemblies. Labeled break and continue statements also simplify exiting nested loops.

• Union types enable exhaustive switch without a default branch
• The closed keyword prevents inheritance from other assemblies
• Labeled break and continue remove the need for flag variables